Most existing methods for localizing a source of electromagnetic signals employ a multi-sensor, dispersed array. Output data from each sensor is a scalar value that corresponds, for example, to the magnitude of the electric field at the sensor. Using such magnitude values, a direction vector can be derived from the array to the source of electromagnetic energy based upon time difference of arrivals. Directionally adjustable single sensors (e.g. rotatable loops) have also been used to derive a vector direction to an electromagnetic source, based upon an orientation of the sensor wherein a maximum signal output is seen. Multi-sensor arrays, because they occupy considerable space, are not well suited to airborne applications or to mobile systems which require limited size antenna sensors. Single sensor systems that rely upon scalar electric field values are slow in response. In the prior art, investigators have designed electromagnetic sensors that detect not only an electromagnetic wave's electric field but also its magnetic field. Kanda et al., in studying the biological effects of electromagnetic radiation, designed loop antenna type sensors to provide simultaneous voltage outputs that gave both electric and magnetic field component values for an incident electromagnetic wave. The resultant field measurements were employed to derive the magnitude of a Poynting vector (a vector that is the power flux density of the field). Kanda et al. used the calculated Poynting vector values to describe an electromagnetic field's energy flow and thus its potential effect on biologic materials. The Kanda et al. work is described in: "An Electromagnetic Near/Field Sensor For Simultaneous Electric and Magnetic/Field Measurements", IEEE Transactions on Electromagnetic Compatibility, Vol. EMC-26, No. 3, 1984, pages 102-110; "An Optically Linked Electric and Magnetic Field Sensor For Poynting Vector Measurements In The Near Fields of Radiating Sources", IEEE Transactions on Electromagnetic Compatibility, Vol. 30, No. 4, November 1988, pages 495-503; and "A Three-Loop Method For Determining the Radiation Characteristics of an Electrically Small Source", IEEE Transactions on Electromagnetic Compatibility, Vol. 34, No. 1, February 1992, pages 1-3.
It is an object of this invention to provide a method for determining a direction to a source of electromagnetic radiation in a noisy environment, such method employing a lumped vector sensor.
It is another object of this invention to provide an improved method for determining a direction of arrival (DOA) of an electromagnetic wave in a noisy environment, the method employing both electric and magnetic field measurements.
It is yet another object of this invention to provide a improved method for determining the DOA of an electromagnetic wave that is suited to airborne and mobile applications.